The proposed study of cardiac innervation is designed to provide useful information on both the structure and function of the cardiac nerves. Fluorescence microscopy will be used to visualize adrenergic cardiac nerves: A thiocholine technique will be used for acetylcholinesterase-containing elements. The distribution of motor and sensory nerves within the heart will be mapped out using a degeneration technique. The reflexogenic zones of the heart also will be located and their central connections explored with the aid of exogenous protein markers. Morphologic relationships between adrenergic, acetylcholinesterase-containing and sensory nerves will be studied under the electron-microscope. The innervation of coronary arteries and veins will be studied using the techniques mentioned above.